Power assisted actuator



y 1962 E7 E. PRATHER 3,031,850

POWER ASSISTED ACTUATOR Original Filed Jan. 7, 1955 3 Sheets-Sheet 1 INVEN TOR.

BYEDWIN E.PRATHER M 5 mm ATTORNEY May 1, 1962 E. E. PRATHER POWERASSISTED ACTUATOR 3 Sheets-Sheet 2 Original Filed Jan. 7, 1955 INVENTOR.gowm E. FEATHER ATTORNEY May 1, 1962 E. E. PRATHER 3,031,850

POWER ASSISTED ACTUATOR Original Filed Jan. 7, 1955 5 Sheets-Sheet 3INVENTOR. iowm E. FEATHER ATTORNEY 3,031,850 POWER ASSISTED ACTUATOREdwin E. Prather, South Bend, Ind, assignor to The liendix Corporation,a corporation of Delaware Continuation of abandoned application Ser. No.489,575, Jan. '7, 1955. This application Feb. 10, 1958, Ser. No.

12 Claims. (Cl. Gil-54.6)

atent ble,it is imperative from the standpoint of safety that a manualbraking system be available which operates efficiently, requiring aminimum pedal eifort to obtain optimum braking conditions. Most powerassisted actuators incorporate a constant area plunger in themastercy'linder, which when power assistance is unavailable requires anincrease of operator effort at the brake pedal to deliver apredetermined amount of fluid to the brake system. Generally, in thecase of automotive brakes, it is necessary that the brake shoes be firstmoved outwardly until they engage the brake drum, at which time theywill begin to do the work for which they were intended. The initialmovement of the shoes take up the shoe to drum clearance withoutperforming any braking action.

The amount of force required to move the shoes into contact with thedrum is relatively small, though the actual movement of the shoes may bea considerable amount. For the first movement of the shoes, therefore, arelatively large amount of hydraulic fluid is required, and this may beat a relatively low pressure; whereas after the shoes have engaged thedrum, the movement of the shoes is quite small but a considerable forcemust be exerted, and therefore a small amount of hydraulic fluid under arelatively high pressure is required. While all of the fluid might besupplied to the brake shoe operating mechanism at a relatively highpressure, this is unnecessary and at times even undesirable.

When power assistance is available there is generally no probleminvolved in regard to the pressure at which the fluid will be deliveredto actuate the brake shoes inasmuch as any extra effort required will besupplied through the medium of the pressure differential created by theaforementioned vacuum created by the intake manifold. However, whenpower assistance is unavailable, it has been found preferable to providetwo rates offlow of hydraulic fluid to the brake operating cylinders orservo-mechanism, the first flow being of a relatively large quantity offluid at a relatively low pressure to move the brake shoes intoengagement with the brake drums, and then to provide a relatively smallflow of fluid at a relatively high pressure. In this way the operator isbetter able to feel the action of the brakes, at no power conditions andan excessively large movement of the brake pedal is not necessary.

In operation, the amount of fluid at relatively low pressures necessaryto move the shoes into contact with the brake drum will vary as thebrake shoes wear. The amount of low pressure fluid necessary to chargethe brake operating mechanism, as distinguished from the high pressurefluid necessary to apply the brakes, will thus vary so that a devicewhich always delivers a constant amount of char ing fluid beforedelivering the operating fluid may at times prove unsatisfactory.

Therefore a primary object of this invention is to provide in a powerassisted braking system a master cylinder ice which will furnish duringbrake actuation at a no power condition, a charge of fluid underrelatively low pressure and of suflicient volume to take up shoe to drumclearances, and thereafter supply a lesser volume of fluid at a higherpressure to insure optimum brake performance.

A further object of this invention is to provide a master cylinder in apower assisted brake system which, during brake actuation at no powerconditions, will compensate for changing volumetric requirements of thebrake system to enable optimum manual actuation of the brake system andnecessitate a minimum of pedal etiort.

Another object of tins invention is to provide in a braking systemincorporating a power assisted actuator a master cylinder for makingavailable under power condition a constant plunger displacement area,and under no power condition a variable plunger displace ment area,depending upon volumetric requirements of the brake system.

It is still further object of this invention to provide in a powerassisted brake system, a secondary manually operated brake system whichis simple and efficient, requiring the minimum of effort to obtainoptimum braking conditions.

The foregoing and other objects and. advantages of the invention will beapparent from the following detailed description considered inconnection with the accompanying drawings, submitted for the purpose ofillustration and not intended to define the scope of invention,reference being had for that purpose to the subjoined claims.

In the drawings, wherein similar reference characters refer to similarparts throughout the several Views:

FIGURE 1 is a schematic view of a combined manual and power-assistedhydraulic braking system showing the power actuator partially brokenaway;

FIGURE 2 is an enlarged longitudinal. sectional View, partially in planshowing the valve structure of the power actuator;

FIGURE 3 is a further enlarged partial longitudinal sectional view ofthe novel master cylinder structure when power assistance is available;and

FIGURE 4 is a fragmentary view of the novel master cylinder structuresimilar to that of FIGURE 3, during no power conditions wherein powerassistance is unavailable.

Referring to the drawings and more particularly to FIGURE 1, apower-assisted actuator unit 12 is secured directly to the enginecompartment side of a toe-board 14. The toe-board forms the slantinglower portion of the fire wall which separates the drivers compartment16 from the engine compartment 18. The power-assisted actuator 12includes a power cylinder 20 and a hydraulic pressure cylinder 22mounted on the end of the power cylinder. The power cylinder casing maybe secured by means of fastening members 24, to the toe-board or anyother part of the vehicle.

The power assisted actuator 12 is controlled by a treadle 28, which ispivoted at 30 on the drivers compartment side of the fire wall. Thetreadle may be pivoted at its lower end, similarly to a conventionalaccelerator treadle, if preferred. A control rod 32 is pivotallyconnected at 34- to the treadle 28, and extends into the power-assistedactuator to control its operation. As shown in FIGURE 2, the right handend of rod 32 operatively engages a valve control member or plunger 36.Reciprocably received in cylinder 20 is a power piston or pressureresponsive movable wall 38 which defines in said cylinder two variablevolume chambers 5-0 and 42. This piston 38 is provided with an internalcavity which is divided into compartments 44 and 46 by means of apressure responsive diaphragm 48. The piston 33 is comprised of twoplates 50 and 52 peripherally joined together in any suitable manner.Communication passages are provided between chamber 40 and compartment46 and rear chamber 42 and front compartment 44. The plate member 50includes an integral rearwardly extending portion 54 which supports asleeve member 56 in which the control plunger 36 is slidably received.Control plunger 36 and sleeve member 56 include cooperating lands andcontrol ports to form a slide valve for controlling pressuredifferential across the power piston 38 which is effective to act on thediaphragm member 48 to apprize the operator of the braking effort. Theaforementioned structure is described in detail in the copendingapplication of Earl R. Price, Serial No. 411,386, filed February 19,1954, now Patent No. 2,818,710. It should be noted that the controlvalve and reaction structure referred to in application Serial No.411,386 forms no part of the present invention and could readily bereplaced by other control valves and reaction structure.

Any desired type of differential fluid pressure power device may beused, and the unit may be either atmosphere-suspended orvacuum-suspended. In this instance an atmosphere-suspended unit isdisclosed wherein the necessity for sealing oif chamber 42 andcompartment 44 from the atmosphere is obviated.

The valve control plunger 36 respectively controls the communication ofcompartment 46 (hence also chamber 40) with either the atmosphere inchamber 42, or a source of vacuum, such as the usual intake manifold 58.The intake manifold 58 is in communication with slide valve structure bymeans of a conduit 60.

The diaphragm member 48 includes a centrally located cushioning button62 which is held in engagement with the right end 64 of the controlplunger 36 by means of a coiled spring 65 interposed between thecushioning button 62 and the inner wall 66 of the piston plate portion52.

A pressure of force transmitting member 68 projects through an opening70 in the end 72 of cylinder 20 and extends into the pressure chamber74. The power piston plate member 52 is provided with a centrallylocated socket 76 which supports the left end of the force transmittingmember 68. The piston 38 is urged toward a released position by means ofa spring 78 interposed between the front end 72 of the power cylinder 20and a retainer ring 80 suitably secured to the left end of forcetransmitting member 68. The retainer ring 80 overlies and is urged inthe direction of centrally located socket 76. Thus the force of spring78 is transmitted to piston 38 through the intermediary f the left endof rod 68.

A suitable seal assembly 82 is provided on member 68 in pressure chamber74 to prevent leakage between chamber 74 and chamber 40.

The hydraulic pressure cylinder 22 is provided with an outlet port 84through which the fluid pressure created in pressure chamber 74 iscommunicated through conduit 86 to brake wheel cylinders 88 (only onebeing shown) to actuate the brake shoe assemblies 90. A fluid reservoir92 replenishes and compensates the hydraulic system with fluid. Thereservoir 92 is in communication with the pressure chamber 74 via outlet94 in which a valve 96 is located. The valve 96 includes a dependingstem 98 projecting into the interior of chamber 74 where it is engagedby a flange 100 secured in any suitable manner on the end portion of thethrust transmitting member 68 which extends into chamber 74. When thethrust transmitting member is urged to its leftmost position under theaction of spring 78, the flange member 100 will normally contact thestem 98 tilting the valve off its seat and permitting communicationbetween reservoir 92 and the interior of pressure chamber '74. Containedin the outlet 84 between the brake assemblies and the pressure chambers74 is a suitable residual check valve 102 for maintaining a residualline pressure in the brake system.

The structure heretofore described is substantially that disclosed inthe previously mentioned Price application and does not per seconstitute applicants invention.

As clearly seen in FIGURES 3 and 4 the thrust transmitting member may becharacterized as a volumetric plunger which, when moved to the right,will tend to decrease the volume in pressure chamber 74 of cylinder 22thereby providing means for pressurizing any hydraulic fluid containedin chamber 74 which will be directed to the brake cylinders aspreviously mentioned.

The thrust transmitting member 68 has an end 104 of tubular constructionwhich extends into the chamber 74. A fluid chamber 105 is formed withinthe tubular portion 104 to which the flange is secured. The tubularportion forming the chamber is closed by end Wall 106 and open at 107.As viewed in FIGURE 3, fluid displacement in chamber 74 due to therightward movement of force transmitting member 68 can be said to besubstantially equal to the distance the thrust transmitting member 68 ismoved into chamber 74 (or length of stroke) times the cross-sectionalareas of end wall 106 and that of the tubular end portion or annulus104. Thus it may be said that the force transmitting member includes twoeifective displacement portions constituted by the crosssectional areasof chamber 105 (this being the same as the area of end wall 106) andthat of annular or tubular portion 104.

A valve housing 108 is located at one end of the power cylinder 20; saidvalve housing containing valve structure 110 which is operable to permitfluid displacement by both displacement portions of the forcetransmitting member 68, Le. the effective cross-sectional areas of endwall 106 and tubular portion 104 during power-on condition, andsequential fluid displacement by said displacement portions duringpower-oil? conditions.

The housing 108 is provided with a bore 112 in which a hollowcylindrical valve plunger member 114 is reciprocably received. Formed inhousing 108 in communication with bore 112 and pressure chamber 74 arepassages 116 and 118 connected by a passage 120. Integral with orotherwise suitably secured to the inner wall 122 of pressure chamber 74is a tubular rod member 124 having a free end 126 which is slidablydisposed in chamber 105 of the force transmitting member 68. A suitableseal means 128 is provided on the exterior of rod 124 contained inchamber 105 to prevent leakage between chambers 105 and 74. Tubular rodmember 124 has an internal passage 130 in communication with a passage132 in the valve housing 108 and permits communication between chamber105 and bore 112 of the valve housing. Thus it can be readily seen thatrightward movement of the force transmitting member 68 causes fluid tobe displaced by the effective cross-sectional area of end wall 106through passage 130 into the bore 112 of the valve housing member.

Housing 108 includes an additional internal passage 134 which connectsthe bore 112 with conduit 136 at 138 to permit transmittal of fluidtherethrough to the reservoir 92.

As shown in FIGURE 4, a pressure chamber 140 is formed in the housingmember 108 at one end of the valve plunger 114. The chamber 140communicates with the chamber 74 via passages 116, 118, and 120. Thevalve bore 112 includes annular channels 142, 144, and 146 incommunication with passages 118, 132, and 134, respectively, in theposition shown in FIGURE 4. Suitable seal means 148 are included on eachside of the aforementioned annular chambers to prevent fluid pressureleakage therebetween in bore 112 past valve plunger 114.

The valve plunger 114 includes a hollow center chamber 150 having spacedradially extending passages 152, 153, and 154; passages 153 and 154being diametrically opposite each other. In the position shown in FIGURE3, passages 152, and 154 are in communication with passages 132 and 118,respectively and fluid through passage 153 is blocked off by channel144. The valve plunger, as shown in FIGURE 4, reciprocates to permitpassage 154 to be in communication with passage 132, and passage 153 tocommunicate with passage 134, thus providing a conlower portion 160 orthe valve plunger 114, which when engaged therewith assures alignment ofpassages 152 and 154 with passages 132 and 118, respectively.

Secured to the stop member 158 in any suitable manner is a pressureresponsive diaphragm member 162 which forms with an annular recessportion 164 of the housing member 1118 adjacent to the valve bore 112 acompartment 166. The compartment 166 includes a passage 168 I connectedto a conduit 170 which is in communication with the intake manifold 58,as shown in FIGURES l and 3. interposed between the diaphragm .162 andthe opposite wall 172 of the compartment 166 is a spring 174 which urgesthe stop member 158 toward the right or away from engagement with avalve plunger 114. Wall 172 includes an integral tubular extension 173which serves as a stop for plunger 158 to prevent excessive leftwardmovement in the position shown in FIGURE 3 as Well as a support forplunger 158. The diaphragm 162 is secured about its periphery by meansof a cap member 176 held in place by means of screws 178, for example.The cap member 176 contains an aperture 180, thus permitting atmosphericpressure to be available on the side of the diaphragm oppositecompartment 166 at all times.

Contained in the end of valve bore 112 opposite chamber 1451 is a valveplunger adjusting and stop assembly 182. This assembly consists of abushing member 184 which is threaded into the bore 112 and includes atubular extension 186 which is of a predetermined length to establishalignment between the passage 154 and the passage 132 when the plunger114 is in the position shown in FIGURE 4. An adjusting screw 188 iscentrally threaded into the bushing 184. A spring 190 is interposedbetween the lower portion 16b of the valve plunger 114 and the internalend 192 of the adjusting screw 188, biasing the plunger against stop191.

The stop member 158 by virtue of its connection with diaphragm 162 isurged toward the left to the extent permitted by stop 173, into anabutting position with the plunger 114 when a source of vacuum isavailable from the intake manifold. In the event of power failure orloss of a source of vacuum, the spring 174 urges the stop member 158into contact with cap member 176, as seen in FiGURE 4, out of engagementwith the lower portion 16-11 of the plunger 114, thus permitting theplunger to move downwardly in the bore 112. However, downward movementof the plunger 114 is prevented by the spring 1% w ich retains theplunger in the position illustrated in FIGURE 3 until sufficientpressure is created in chamber 1411 to overcome the force of spring1911.

Operation of the device of the invention during poweron conditions is asfollows:

1 Attention is now directed to the position of the structure disclosedin FIGURE 3 of the drawing wherein the position of the parts are shownwhen a source of vacuum is available. Depression of the treadle 28 willcause relative movement between valve plunger 36 and valve sleeve 56causing a pressure ditlerential across the power piston 38. Inasmuch asvacuum source is available during power-on conditions a pressuredifferential will exist at this time across the diaphragm 162 urging thestop member 158 intoits illustrative position in abutment with the lowerportion 16b of the valve plunger 114 but prevented by tubular extension173 from striking spring 190. With the development of a pressurediiferential across power piston 38 movement of the force transmittingmember 68 into the pressure chamber 74 is accomplished. The resultingmovement of the force transmitting member causes fluid to be displacedby the eifective displacement portions of the cross-sectional area ofend wall 106 and the cross-sectional area of the tubular portion 104.The fluid displaced by the effective portion of 104 is pushed out theoutlet 84 and to the wheel cylinders 83 of the brake system.Simultaneously fluid from this effective portion of the forcetransmitting member is urged through passage 118, 120, and 116 tochamber 14-0 and is eliective to tend to urge the plunger 114 to adownward position. However, inasmuch as stop member 153 is in engagementwith the lower portion 160 of the plunger member 114 this pressureexisting in chamber causes no movement of the valve plunger. At the sametime, the elrective displacing portion of end wall 106 causes fluid tobe urged through passage 130, 132, and 152 into the internal chamber ofplunger member 114 out of passage 154 through passage 118 and thence outof passage 84 to the wheel cylinders 88. Thus in the positionillustrated in FIGURE 3, the entire efiective displacement portion ofthe force transmitting member 63 is efiective to transmit fluid pressureto the brake system.

Operation during power-off? conditions is as follows:

During a power-o condition, see FIGURE 4, where in a source of vacuum isunavailable, actuation of the treadle 28 and movement of the plunger 36therewith causes the member 62 to be urged into contact with the innerwall 66 of power piston 38 and any fluid displacement in the brakesystem is accomplished only by the physical effort imposed by theoperator of the brake system. At this time, since there is no vacuum inchamber 166 the spring 174 is effective to urge the stop member 158toward the right into contact with the inner side of cap 176 and out ofcont-act with the lower portion of the valve plunger 114. However, thespring is of suflicient strength to urge the valve plunger passages 152and 154 into alignment with passages 132 and 118, respectively, topermit the passage of fluid in the manner described during power-011conditions.

During initial brake actuation wherein a relatively low pressure isrequired to take up brake-to-drum clearances, the low pressure isinsuthcient to build up a pressure in chamber 140 to cause the plunger114 to move downwardly against the stop member 186. During this firststage, fluid is displaced by both efiective portions of the end wall1116 and the effective cross-sectional portion of tubular member 104until the brake system demands a relatively higher pressure to beexerted at the brake cylinders to cause deceleration of the vehicle.With the demand for a higher pressure and a comparable demand for anincreased output of physical effort on the operators part, comes anincrease of fluid pressure in chamber 141) causing the plunger 114 tomove downwardly, overcoming the force of spring 190 and at this timepassage 15 4 becomes aligned with passage 132. Fluid displaced by theelfective cross-sectional area of end wall 196 is then directed outpassage 130, through passage 132, and through passage 154 into thecompartment 150. Inasmuch as plunger 114 has moved downwardly, passage152 is now in alignment with pass-age 134 which communicates with thefluid reservoir 92 and thus fluid displaced by the effective displacement area of end wall 106 is directed to the fluid reservoir.

Release of pressure on the treadle 28 by the operator results in theremoval of pressure in chamber 140 and thus spring 190 will be effectiveto urge plunger 114 back to the position disclosed in FIGURE 3. When apower source is again available, the pressure differential will becomeavailable across diaphragm 162 and will be sun cient to overcome spring174 and urge the stop member 158 into engagement with the lower portion16% of valve plunger 114.

Thus it can be seen that the power assisted brake system is providedwith an alternative brake system during power-off conditions whereinpressure cylinder-valvecompounding structure permits fluid displacementto a brake system depending upon volumetric requirements of the brakesystem.

Although a particular embodiment of the invention has been illustratedand described other changes and modifications will be apparent to thoseskilled in the art. All changes and modifications falling within thescope of the claims are intended to be claimed.

I claim:

1. In an automotive hydraulic braking system and the like: a drivenfluid pressure motor; first and second fluid displacement means;servomotor means for simultaneously actuating said first and secondfluid displacement means; a power source for operating said servomotor;means for simultaneously actuating said first and second fluiddisplacement means by manual force when power is not available toactuate said servomotor means; exhaust passage means for receiving fluidfrom said first fluid displacement means at a low pressure; valve meanshaving a movable element which when in a first position closes off saidexhaust passage means from said first fluid displacement means whilecommunicating said first displacement means to said driven fluidpressure motor, and when in a second position closes ofi said firstfluid displacement means from said driven fluid pressure motor whilecommunicating said first fluid displacement means to said exhaustpassage means; means for moving said movable element from said first tosaid second position when the pressure in one of said displacement meansexceeds a predetermined value; and fluid pressure motor means operatedby said power source for holding said movable element in said firstposition when power is available to operate said servomotor means.

2. In an automotive hydraulic braking system and the like: first andsecond fluid displacement means; servomotor means for simultaneouslyactuating said first and second fluid displacement means; a power sourcefor operating said servomotor; means for simultaneously actuating saidfirst and second fluid displacement means by manual force when power isnot available to actuate said said servomotor means; exhaust means forreceiving fluid from said first fluid displacement means at a lowpressure; first valve porting means for communicating fluid from saidfirst fluid displacement means to a driven fluid pressure motor when thepressure in said first fluid displacement means is at least as great asthe pressure in said second fluid displacement means; and second valveporting means having a movable element which when in a first positioncloses ofi said first fluid displacement means from said exhaust meansand when in a second position communicates said first fluid displacementmeans to said exhaust means; means for holding said movable element insaid first position when the pressure in said second fluid displacementmeans is below a predetermined value and for moving said movable elementto said second position when the pressure in said second fluiddisplacement means exceeds said predetermined value; and a fluidpressure motor communicating with said power source for holding saidmovable element in said first position when power is available toactuate said servomotor means.

3. In an automotive hydraulic braking system and the like: first andsecond fluid displacement means; servomotor means for simultaneouslyactuating said first and second fluid displacement means; a power sourcefor operating said servomotor; means for simultaneously actuating saidfirst and second fluid displacement means by manual force when power isnot available to actuate said servomotor means; exhaust means forreceiving fluid from said first fluid displacement means at a lowpressure; first valve porting means for communicating fluid from saidfirst fluid displacement means to a driven fluid pressure motor; secondvalve porting means having a movable element which when in one positioncloses oft said first fluid displacement means from said exhaust meansand which when in a second position opens communication to said exhaustmeans; said first valve porting means be- 8 ing constructed and arrangedso that it is closed when fluid passes out through said second valveporting means; fluid pressure motor means for moving said movableelement from its first position to said second position when thepressure in said second fluid displacement means exceeds a generallypredetermined level; and fluid pressure motor means controlled by saidpower source for holding said movable element in its first position whenpower is available to actuate said servomotor means.

4. In an automotive hydraulic braking system and the like: first andsecond fluid displacement means; servomotor means for simultaneouslyactuating said first and second fluid displacement means; a power sourcefor operating said servomotor; means for simultaneously actuating saidfirst and second fluid displacement means by manual force when power isnot available to actuate said servomotor means; exhaust means forreceiving fluid from said first fluid displacement means at a lowpressure; first valve porting means for discharging fluid from saidfirst fluid displacement means into the discharge of said second fluiddisplacement means; second valve porting means having a movable elementwhich when in one position closes off said first fluid displacementmeans from said exhaust means and which when in a second position openscommunication to said exhaust means; said first valve porting meansbeing constructed and arranged so that it is closed when said secondvalve porting means is opened; fluid pressure motor means for movingsaid movable element from its first position to said second positionwhen the pressure in said second fluid displacement means exceeds agenerally predetermined level; stop means which when in one positionpermits said movable element to move from its first position to itssecond position and which stop means when in a second position holdssaid movable element in its first position; and fluid pressure motormeans for holding said stop means in its second position when power isavailable to actuate said servomotor means.

5. In an automotive hydraulic braking system and the like: first andsecond fluid displacement means each having a discharge port; servomotormeans for simultaneously actuating said first and second fluiddisplacement means; a power source for operating said servomotor; meansfor simultaneously actuating said first and second fluid displacementmeans by manual force when power is not available to actuate saidservomotor means; exhaust means for receiving fluid at a low pressure;valve means connected to the discharge port of said first fluiddisplacement means, said valve means having a control element which whenin one position communicates said discharge port of said first fluiddisplacement means to an outlet port for actuating a driven fluidpressure motor, and which when in a second position communicates saiddischarge port to said exhaust means; fluid pressure means actuated bypressure from said second fluid displacement means for moving saidcontrol element from said first position to said second position whenthe pressure in said second fluid displacement means exceeds a generallypredetermined pressure; and means for holding said control element insaid first position when power is available to actuate said servomotormeans, and for permitting said control element to be moved to its secondposition when power is not available to actuate said servomotor means.

6. In an automotive hydraulic braking system and the like: first andsecond fluid displacement means each having a discharge port; servomotormeans for simultaneously actuating said first and second fluiddisplacement means; a power source for operating said servomotor; meansfor simultaneously actuating said first and second fluid displacementmeans by manual force when power is not available to actuate saidservomotor means; exhaust means for receiving fluid at a low pressure;valve means connected to the discharge port of said first fluiddisplacement means, said valve means having a control element which whenin one position communicates said discharge port of said first fluiddisplacement means to the 9 discharge of said second fluid displacementmeans, and which when in a second position communicates said' dischargeport to said exhaust means; fluid pressure means actuated by pressurefrom said second fluid displacement means for moving said controlelement from said first position to said second position when thepressure in said second fluid displacement means exceeds a generallypredetermined pressure; and means for holding said control element insaid first position when power is available to actuate said servomotormeans, and for permitting said control element to be moved to its secondposition when power is not available to actuate said servomotor means.

7. In an automotive hydraulic braking system and the like: first andsecond fluid displacement means each having a discharge port; servomotormeans for simultaneously actuating 'said first and second fluiddisplacement means; a power source for operating said servomotor; meansfor simultaneously actuating said first and second fluid dis placementmeans by manual force when power is not available to actuate saidservomotor means; exhaust means for receiving fluid at a low pressure;valve means connected to the discharge port of said first fluiddisplacement means, said valve means having a control element which whenin one position communicates said discharge port of said first fluiddisplacement means to said second fluid displacement means, and whichwhen in a second position communicates said discharge port to saidexhaust means; fluid pressure means actuated by pressure from saidsecond fluid displacement means for moving said control element fromsaid first position to said second position when the pressure in saidsecond fluid displacement exceeds a generally predetermined pressure;stop means which when in one position permits said movable element tomove from its first position to its second position and which stop meanswhen in a second position holds said movable element in its firstposition; and fluid pressure motor means for holding said stop means inits second position when power is available to actuate said servomotormeans.

8. In an automotive hydraulic braking system and the like: first andsecond fluid displacement means each having a discharge port; servomotormeans for simultaneously actuating said first and second fluiddisplacement means; a power source for operating said servomotor; meansfor simultaneously actuating said first and second fluid displacementmeans by manual force when power is not available to actuate saidservomotor means; exhaust means for receiving fluid at a low pressure;valve structure having a cylindrical bore therein with a movable slidevalve in sealing engagement with the side walls of said bore, said slidevalve having porting which when in one position adjacent one end of saidvalve bore communicates said discharge port of said first fluiddisplacement means to said second fluid displacement means, and whichwhen in a second position communicates said discharge port to saidexhaust means; spring means biasing said slide member toward said oneend of said valve bore; fluid passage means communicating fluid pressurefrom said second fluid displacement means to said one end of said valvebore; stop means which when in one position permits said slide member tomove from its first position to its second position and which stop meanswhen in a second position holds said slide member in its first position;and fluid pressure motor means for holding said stop means in its secondposition when power is available to actuate said servomotor means.

9. In an automotive hydraulic braking system and the like; a body memberhaving a fluid pressurizing chamber therein; a tubular fluiddisplacement member projecting into one end of said fluid pressurizingchamber; a tubular plunger member projecting from the other end of saidfluid pressurizing chamber into the internal chamber of said tubularfluid displacement member to displace fluid therefrom through saidplunger member; servomotor means for forcing said tubular fluiddisplacement member into said fluid pressurizing chamber over saidplunger member; a power source for operating said servomotor; means forforcing said tubular fluid displacement member into said fluidpressurizing chamber over said plunger member by manual force when poweris not available to actuate said servomotor means; exhaust means forreceiving fluid at a low pressure; first valve porting means forcommunicating fluid discharged from said tubular plunger to said fluidpressurizing chamber, second valve porting means having a movableelement which when in one position closes communication from the insideof said tubular plunger member to said exhaust means and which when in asecond position opens communication to said exhaust means; said firstvalve porting means being constructed and arranged so that it is closedwhen fluid passes out through said second valve porting means to saidexhaust means; fluid pressure motor means for moving said movableelement from its first position to said second position when thepressure in said fluid pressurizing chamber exceeds a generallypredetermined level; stop means which when in one position holds saidmovable element in its said one position, and which stop means when in asecond position permits said movable element to move from its firstposition to its second position; and fluid pressure motor means forholding said stop means in its first position when power is available toactuate said servomotor means.

10. In an automotive hydraulic braking system and the like; a bodymember having a first fluid pressurizing chamber therein; a tubularfluid displacement member projecting into one end of said fluidpressurizing chamber; a tubular plunger member projecting from the otherend of said fluid pressurizing chamber into the internal chamber of saidtubular fluid displacement member; servornotor means for forcing saidtubular fluid displacement member into said fluid pressurizing chamber;a power source for operating said servomotor; means for forcing saidtubular fluid displacement member into said fluid pressurizing chamberby manual force when power is not available to actuate said servomotormeans; exhaust means for receiving fluid at a low pressure; acylindrical valve bore in said body member having a slide member insliding sealing engagement with the side walls of said bore, said slidemember having suitable passages therein for communicating the inside ofsaid tubular plunger member to said fluid pressurizing chamber when saidslide member is in a first position adjacent one end of said cylindricalvalve chamber and for communicating the inside of said tubular plungermember to said exhaust means when said slide member is in a secondposition away from said end of said cylindrical valve bore; spring meansbiasing said slide member towards said one end of said valve bore; fluidpassage means communicating said fluid pressunzing chamber to said oneend of said cylindrical valve bore; stop means which when. in oneposition holds said slide member in its said one position, and whichstop means when in a second position permits said slide member to movefrom its first position to its second position; and fluid pressure motormeans for holding said stop means in its first position when power isavailable to actuate said servomotor means.

11. In a force transmitting system for actuating brakes and the like: amanually actuatable driving member and a driven member; forcetransmitting means for transmitting force from said driving member tosaid driven member, said force transmitting means having a firstcondition for transmitting force to said driven member with a lowmechanical advantage, and a second condition for trans mitting force tosaid driven member with a high mechanical advantage; a servomotor forapplying force to said driving member, said servo-motor being adapted tobe powered by a fluctuatable source of power; control means which whenin a normal condition causes said force transmitting means to be in itsfirst condition and which when a-predetermined force is applied throughsaid force transmitting means shifts said force transmitting means toits second condition; and motor means adapted to be actuated by saidpower source for said servomotor, said motor means holding said controlmeans in its normal position and preventing said force transmittingmeans from moving to its second condition when the energy level of saidpower source is above a predetermined level and releasing said controlmeans to function normally when said energy level is below saidpredetermined level.

12. In a fluid pressurizing unit having an outlet connection: first andsecond fluid displacement means; servomotor means for simultaneouslyactuating said first and second fluid displacement means, saidservomotor being driven by a fluctuatable power source; means forsimultaneously actuating said first and second fluid displacement meansmanually; exhaust passage means for receiving fluid at a low pressure;valve means communicating said first fluid displacement means to saidoutlet connection when in one condition and communicating said firstfluid displacement means to said exhaust passage means when in a secondcondition; said valve means normally being in its first condition; fluidpressure means for moving said valve means into its second conditionwhen the References Cited in the file of this patent UNITED STATESPATENTS 1,084,715 Steinmann Jan. 20, 1914 1,903,973 Boughton Apr. ,18,1933 2,031,360 Boughton Feb. 18, 1936 2,190,238 Lepersonne Feb. 13, 19402,331,238 Schnell Oct. 5, 1943 2,402,344 Price June 18, 1946 2,875,582Hill Mar. 3, 1959 FOREIGN PATENTS 747,273 France Mar. 28, 1933

